1. Field:
The invention is in the field of screen printing machines and in particular, of platen assemblies used in such machines for printing articles of clothing, such as tee shirts or the like.
2. State of the Art:
Screen printing of designs onto articles of clothing is a common practice. Most simply, an article of clothing, such as a tee shirt, is placed upon a flat surface, a silk screen is positioned on the tee shirt, and then ink is transfered through the screen onto the tee shirt by means of a roller or squeegee. When several colors are to be printed on the tee shirt, a number of silk screens are used, each silk screen being used with a different color. However, each subsequent silk screen must be aligned with the previously printed design for a satisfactory final product. Machines are now available to accommodate multiple screens and provide for registration and alignment of the individual designs on these multiple screens on a single tee shirt.
With presently used machines, the tee shirt to be printed is placed around a printing platen so that there is only a single layer of material between the platen and the silk screen. A thin layer of spray adhesive is applied to the platen immediately prior to placing the tee shirt thereon in order to hold the tee shirt essentially immovable on the platen during the screen printing processes. This not only holds the shirt against movement during actual printing which could cause smearing of the ink, but also, with multi-color printing, maintains the shirt in proper alignment and registration with respect to the different color silk screens so that the resulting multicolored design on the tee shirt will be in proper alignment with no color voids, overlaps, or blurrs.
A relatively recent concept in screen printed tee shirts is what is called in the trade a "wrap-around" design. This particular type of design wraps completely around the body portion of the shirt and appears to be a continuous design extending around the shirt. Complicated and expensive printing machines for printing these "wrap-around" designs onto tee shirts have been developed by one shirt manufacturer, but the cost of such machines prohibits their use in relatively low volume screen printing enterprises, such as custom printing shops. Such type of expensive wrap-around design printing apparatus involves placing the tee shirt about a cylindrical shaped platen, and then using a cylindrical shaped printing drum to print a continuous, wrap-around design onto the tee shirt.
Attempts have been made to print "wrap-around" designs onto tee shirts by using a flat printing platen or table. This process involves printing half of the wrap-around design onto one side of the tee shirt, either the front or the back, followed by printing the second half of the wrap-around design on the opposite side of the tee shirt. Although this may sound simple in theory, unless the alignment and registration of the front and back patterns are exact at both edges of the tee shirt where the designs meet (usually under the sleeves), misalignment occurs and the resulting pattern is not the intended "wrap-around" design but rather is a tee shirt having misaligned and disjointed front and back patterns.
The problem is compounded where multi-color wrap-around designs are attempted. This is because with a shirt merely placed on a flat surface, there is nothing to hold the top layer of material of the shirt and when the silk screen for the first color is raised from the garment, the garment tends to stick to the silk screen and be pulled up slightly when the silk screen is removed from the garment. As the shirt falls back to the platen, it may shift position slightly destroying any alignment or registration. Once the registration is lost, it is difficult to accurately realign or reregister the first color pattern on the shirt with subsequent colored patterns. Although it may be possible to closely reregister the garment on the printing platen to accept subsequent multi-color silk screens, such process is extremely time consuming and tedious, therefore greatly increasing production costs of a single multi-color, wrap-around design tee shirt.